The present invention relates to environmental chambers that are used to control the environment surrounding a test specimen. More particularly, the present invention provides a gaseous convection environmental chamber that heats or cools a limited portion of the test specimen.
Commonly, during the testing of material specimens, for example, such as tensile and compressive loading, the specimen to be tested is placed in an environmental chamber. The environmental chamber controls or modifies the environment surrounding the test specimen, and thus, the condition of the specimen itself. By controlling environmental parameters such as temperature and humidity, operating conditions can be simulated in order to determine accurately the performance of the tested material.
Three common techniques are used in environmental chambers to alter the temperature of the test specimen. These techniques include the use of radiant heat energy, induction heat energy, or forced gas or convection heat energy. Briefly, induction heating is the heating of an electrically conducting material by eddy currents induced by a varying electromagnetic field. Radiant heating uses a heat-producing surface that emits heat to the test specimen by radiation rather than by conduction or convection. Environmental chambers that incorporate radiant heating to alter the temperature of a given test specimen include a housing that surrounds either the complete test specimen and the test specimen holding assemblies, or alternatively, a housing that surrounds only a portion of the test specimen. In both forms of radiant heating systems, the radiant heating elements are positioned adjacent the test specimen or a portion thereof in the environmental chamber to localize energy upon the test specimen. Radiant heating, like induction heating, is well suited for heating the test specimen to high temperatures, but neither technique will cool a test specimen to a temperature below the ambient temperature.
In contrast, convection systems are commonly used to either raise and lower the temperature of the test material above or below the ambient temperature. In these known systems, a convection environmental chamber includes a housing that surrounds the test specimen and the test specimen holding assemblies. A fan then moves a gaseous medium, such as air, from a heating or cooling source to the test specimen to obtain the desired operating temperature.
Drawbacks to this type of convection environmental chamber however exist. The most serious drawback is that since the housing surrounds both the test specimen and the test specimen holding assemblies, the test specimen holding assemblies are subjected to the same environment as the test specimen. When high operating temperatures are desired on the test specimen, the standard holding assemblies must be replaced with high temperature holding assemblies manufactured from special alloys and/or equipped with cooling jackets. In either case however, these high temperature holding assemblies are substantially more expensive than the standard holding assemblies, and thus increase the cost associated with testing.